A treatment planning comparison of highly conformal radiation therapy for pediatric low-grade brainstem gliomas

Abstract

To the Editor, The brainstem encompasses the midbrain, pons, and medulla. Brainstem gliomas arise at any age, but most frequently occur during childhood. In children, brainstem gliomas constitute approximately 10–20% of the malignancies affecting the central nervous system (CNS) [1], and the average age at diagnosis is 7–9 years with no gender predilection [2,3]. There are approximately 150–300 new cases diagnosed in USA annually [2]. The diagnosis of brainstem glioma includes a histopathologically diverse number of tumor types, which makes it difficult to assign an overall prognosis [4]. Similar to tumors in other CNS sites, however, low-grade brainstem gliomas are curable with current treatment modalities, whereas high-grade gliomas are often fatal despite aggressive treatment [5]. Of those children diagnosed with brainstem gliomas, approximately 20% are low-grade gliomas [2,3]. There is variability with regard to the resectability of these tumors; however, in general, complete resection is often impossible [2,3,6–8]. External-beam radiation therapy is an accepted and effective treatment modality for patients with unresectable low-grade brainstem gliomas [1,5–8]. When determining the therapeutic ratio, the risks of radiation therapy must be considered along with the potential benefits [9]. As the best 10-year survival rates mandate a relatively high radiation dose deposited in radiosensitive tissue, children treated for brainstem gliomas with radiation therapy are subject to a number of late sequelae, including hearing loss, neuroendocrine deficits, chronic otitis media, neurocognitive dysfunction, and the development of secondary malignancies [9]. There are few contemporary studies in the literature directly addressing the treatment of low-grade pediatric brainstem gliomas. In general, to minimize the risk of late effects in pediatric patients treated with radiation, investigators have historically sought to attenuate the dose to non-target, healthy tissues. For treatment of low-grade brainstem gliomas, recent studies have sought to investigate the role of gamma knife surgery to reduce dose to non-target tissue [10] and therapies of increased conformality, such as photon-based intensity-modulated radiation therapy (IMRT) and proton therapy [11]. Technology facilitating the delivery of highly conformal radiation therapy, such as IMRT and proton therapy, may allow for better sparing of non-target tissues. In this study, we sought to investigate the relative dosimetric features of photon IMRT and proton therapy in the treatment of low-grade brainstem gliomas in order to assess their potential value in reducing late toxicity.